The present invention relates, in general, to reactors used in semiconductor processing and, more particularly, to parallel plate reactors and their method of use.
Typically, semiconductor devices are manufactured by using combinations of differing layers of conductive, insulating, and semiconducting materials. It is often necessary to form openings in an upper substrate layer so that contact can be made with an underlying substrate layer. To accomplish this, a mask is deposited on the substrate. The mask is patterned to cover selected regions while leaving other regions exposed. The wafer is then subjected to a corrosive type of environment which will etch the exposed portion of the substrate. However, the etch materials also tend to etch the masks. It has been an ongoing objective of the industry to develop etching methods and apparatus which will selectively etch substrates. In other words, methods that will etch the substrate at a rate faster than the mask.
By increasing the differences in etch rates between the substrate and mask, the etching can be faster and permit the use of thinner masks. This provides an economic saving to the manufacturer. One type of selective etching is described in U.S. Pat. No. 4,568,410 invented by Stephen C. Thornquist.
Etchers come in two basic types, dry and wet. Wet etchers use a liquid element in which the substrates are submerged in order to etch the substrate. This type of etching is very traumatic and can cause damage to the substrates. Dry etchers use gas which forms a plasma to etch the substrate. Dry etching techniques are often referred to as reactive ion etching or plasma etching. In the prior art types of dry etchers, a plasma is formed by injecting a gas into an area between two electrodes. The reaction of the gas to the RF field produces a plasma which generates ions. The ions then collide with the substrates causing portions of the surface of the substrate to etch, or chip, off.
There are three basic types of reactors that use dry type etching to perform the etching function: barrel reactors, downstream reactors, and parallel plate reactors. The barrel and parallel plate type of reactors etch by generating a plasma envelope (or sheath). The ions generated in this plasma then bombard the substrate which is at a different, generally lower, potential than the electrodes. A disadvantage of these types of etchers is that the substrate is subjected to a much more intense ion bombardment because of the difference in potential between the plasma and the substrate. This makes it much more difficult to vary the etch rate between mask and substrate.
In the downstream reactors, the plasma is generated remotely from the substrate and then by normal diffusion reaches the substrate. A major historical disadvantage of these types of reactors is that they have been made of quartz which is more expensive and more subject to damage than the metal and ceramic type of reactors. Quartz is consumed, or etched away, in a fluorine based etch. This not only damages the chamber but can also leave residue on the substrate.
Accordingly, it is an object of the present invention to provide an improved apparatus and method that will overcome the above noted deficiencies.
A further object of the present invention is to provide a parallel plate reactor and method that improves the selectivity of etch ratios.
Another object of the present invention is to provide a parallel plate reactor which provides the advantages of wet etching in a dry etch environment.
Still another object of the present invention is to provide a parallel plate reactor and method that improves the etch rate.
Yet another object of the present invention is to provide a parallel plate reactor and method that requires a lower ratio of mask to substrate thickness.
Another object of the present invention is to provide a parallel plate reactor and method which improves the selective etching of a fluorine gas sources.
Still another object of the present invention is to provide a parallel plate reactor and method which will selectively etch low pressure chemical vapor deposition (LPCVD) nitride (Si.sub.3 N.sub.4).
Yet another object of the present invention is to provide a parallel plate reactor and method which will etch phosphorous or boron doped oxide, isotropically.